The art of inkjet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, and facsimile machines have been implemented with inkjet technology for producing printed media. Generally, an inkjet image is formed pursuant to precise placement on a print medium of ink drops emitted by an ink drop generating device known as an inkjet printhead assembly. An inkjet printhead assembly includes at least one printhead. Typically, an inkjet printhead assembly is supported on a movable carriage that traverses over the surface of the print medium and is controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to a pattern of pixels of the image being printed.
Inkjet printers have at least one ink supply. An ink supply includes an ink container having an ink reservoir. The ink supply can be housed together with the inkjet printhead assembly in an inkjet cartridge or pen, or can be housed separately. When the ink supply is housed separately from the inkjet printhead assembly, users can replace the ink supply without replacing the inkjet printhead assembly. The inkjet printhead assembly is then replaced at or near the end of the printhead life, and not when the ink supply is replaced.
Some replaceable printer components, such as some inkjet printhead assemblies, include a thermal sense resistor (TSR). A purpose of the TSR is to allow a printer to determine the temperature of the printhead assembly. Knowledge of the consistency of the TSR material allows a thermal coefficient of resistance (TCR) to be determined. The printer can determine the temperature of the printhead assembly based on the TCR and a measured resistance of the TSR.
Generally, the printhead assembly heats up in operation. A printer can monitor the TSR and change the printing algorithm to either add or subtract energy, thereby changing the size of the ink drops coming out. In the case of a cold die (e.g., a new cartridge has just been placed in the printer), the printer will recognize that the printhead assembly is cold and will provide extra energy so that the ink drops become a little bigger. As the die heats up, the printer will provide less and less energy. In some systems, the temperature of the printhead assemblies is monitored to prevent overheating. If the temperature reaches a certain threshold, the printer may go into a wait mode, where the printer pauses briefly to allow the printhead assembly to cool down.
In existing printer systems, analog hardware is used to measure the resistance of the TSR at a known temperature to use as a starting point for later temperature determinations. The initial resistance measurement is an analog measurement, which is not very precise. In addition, the analog measurement hardware is an expensive part of the printer.